Catherine Steadman (born 8 February 1987) is an English actress and author, best known for playing Mabel Lane Fox in series 5 (2014) of ITV drama Downton Abbey. Her debut novel, the psychological thriller Something in the Water, was published in June 2018 by Simon & Schuster UK and Penguin Random House USA.
Steadman trained at the Oxford School of Drama and made her screen debut playing Julia Bertram in the ITV adaptation of Mansfield Park opposite Billie Piper, James D'arcy, Rory Kinnear and Michelle Ryan. Since then she has appeared in television dramas such as the CBC/Showtime co-production The Tudors playing Joan Bulmer, Holby City, Law & Order: UK, Missing, Lewis, Quirke alongside Gabriel Byrne, Fearless opposite Helen McCrory, and Victoria. Most notably she played Nurse Wilson in the ITV drama Breathless, Maggie Lewis in Tutankhamun and Mabel Lane Fox in the 5th series of Downton Abbey. She has also appeared in several comedy series such as The Inbetweeners, Fresh Meat, Trying Again and Bucket.
On stage she has appeared in the West End in shows such as Polly Stenham's award winning That Face opposite Matt Smith and Felicity Jones, which was nominated for a special cast Olivier Award, the Royal Shakespeare Company's production of Oppenheimer, opposite John Heffernan, for which she was nominated for a 2016 Laurence Olivier Award for Best Actress in a Supporting Role, and she played the titular role in the West-end revival of Witness for the Prosecution, opposite David Yelland, which was nominated for a 2018 Laurence Olivier Award for best revival.
She can also be seen in the films Salmon Fishing in the Yemen, Richard Curtis' About Time, Dust, Princess Kaiulani, Astral, and Outpost: Black Sun.